The present invention relates to a novel antifoam composition or, more particularly, to an antifoam composition having excellent foam-breaking and foam-suppressing activity and capable of exhibiting excellent defoaming effect even under violent agitation or even in an alkaline condition of the foaming liquid.
As is well known, silicone-based antifoam agents comprising a dimethylpolysiloxane as the principal ingredient belong to the class of the most widely used antifoam agents useful as a foam-breaking or foam-suppressing agent in chemical industries, food industries, petroleum industries, textile industries, pharmaceutical industries and the like by virtue of the outstandingly superior properties thereof in comparison with other types of antifoam compositions. Even the silicone-based antifoam agent is, however, not almighty and the defoaming activity thereof is sometimes rapidly lost when the foaming liquid admixed with the antifoam agent is violently agitated in contact with air or, in particular, violently agitated at an elevated temperature as in the aeration tank of a sewage disposal plant or in the jet dyeing. This problem is even more serious when the liquid or sewage under the defoaming treatment is in an alkaline condition so that the antifoam agent must be continuously or repeatedly introduced into the foaming liquid or sewage to cause a great economical disadvantage.
Several methods for the improvement of a silicone-based antifoam agent have been proposed in view of the above mentioned problems including, while the silicone-based antifoam agents are usually formulated with a finely divided silica filler, a method in which the silica filler is subjected in advance to a hydrophobic treatment with dimethyl dichlorosilane and the like (see, for example, Japanese Patent Publication No. 52-31836) and a method in which the silica filler is treated with a nitrogen-containing organosilicon compound prior to blending with the silicone (see, for example, Japanese Patent Publication No. 51-35556). These methods for improvements are also not quite satisfactory because the hydrophobic treatment of the silica filler is a complicated and uneconomical process due to the long time taken for the treatment and the necessity of special facilities therefor.
Alternatively, an improved antifoam composition has been proposed which comprises a hydrocarbon oil admixed with an organohydrogenpolysiloxane, a silica filler and a catalyst (see, for example, Japanese Patent Kokai No. 57-48307). The antifoam composition of this type is also not free from several problems and disadvantages that the silica filler must be treated in advance under heating with admixture of an organometallic catalyst in order to obtain a satisfactory effect of surface treatment, that hydrogen gas is always produced in the course of the treatment to cause a danger of fire or explosion and that the defoaming activity thereof is not strong enough in respect of the durability.